Optical sensors that capture a heart rate and/or a blood oxygen content can be realized by virtue of radiating the light from a light-emitting diode onto the skin. In so doing, the light is scattered by tissue below the skin and the intensity of the scattered light can be measured using a photodetector. Some of the radiated-in light is absorbed by hemoglobin molecules in the blood. Blood is pumped through the arteries driven by the heart, with the amount of blood in an artery not being constant, but pulsing with the same frequency as the heart rate. As a result, the amount of blood in the artery varies with the heart rate and the amount of available hemoglobin likewise varies. More of the light of the light-emitting diode, or less, is absorbed by the hemoglobin, depending on whether much or little hemoglobin is in the artery. As a result, the intensity of the scattered light also varies with the heart rate. This changing intensity can be detected by the photodetector. As a result, it is possible to deduce the heart rate from the change of the photocurrent of the photodetector. Such an optical heart rate sensor is known from DE 10 2008 022 920 B4.
There is nonetheless a need to provide an improved optical sensor that determines the heart rate, the sensor moreover being suitable to optionally determine a blood oxygen content.